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Abstract Wind-blown dust from southern South America links the terrestrial, marine, atmospheric, and biological components of Earth’s climate system. The Pampas of central Argentina (~33°–39° S) contain a Miocene to Holocene aeolian record that spans an important interval of global cooling. Upper Miocene sediment provenance based onn = 3299 detrital-zircon U-Pb ages is consistent with the provenance of Pleistocene–Holocene deposits, indicating the Pampas are the site of a long-lived fluvial-aeolian system that has been operating since the late Miocene. Here, we show the establishment of aeolian sedimentation in the Pampas coincided with late Miocene cooling. These findings, combined with those from the Chinese Loess Plateau (~33°–39° N) underscore: (1) the role of fluvial transport in the development and maintenance of temporally persistent mid-latitude loess provinces; and (2) a global-climate forcing mechanism behind the establishment of large mid-latitude loess provinces during the late Miocene. 

Abstract The Tafí del Valle depression (~27° S) in the eastern Andes of Argentina provides a record of late Pleistocene dust deposition in the subtropics of South America. We present large-nU-Pb geochronology data for detrital zircons from upper Pleistocene loess-paleosol deposits. When compared to regional data, the age spectra from the Tafí del Valle samples are most like the southern Puna Plateau, supporting derivation largely from the west and northwest. This runs counter to hypotheses suggesting these loessic sediments were derived from the low elevation plains to the east or extra-Andean Patagonia. Mapping of linear wind erosion features on the Puna Plateau yield a mean orientation of 125.7° (1 s.d. = 12.4°). These new data and existing records are consistent with a westerly-northwesterly dominated (upper- and lower-level) wind system over the southern Puna Plateau (to at least ~27° S) during periods of high dust accumulation in Tafí del Valle. 

The Pampas of Argentina contain a broad distribution of Pleistocene to Holocene loessic sediments and eolian dune deposits. Models describing the sediment provenance of this eolian system have, at times, conflicted. We address the provenance of these deposits through U-Pb detrital-zircon geochronology. Our results indicate broad similarity in age distributions between samples, with a dominant Permian-Triassic mode, and widespread but lesser Cenozoic, Devonian-Mississippian, Ediacaran-Cambrian, and Mesoproterozoic modes. These data are inconsistent with a large contribution of detritus from Patagonia as previously suggested. These data are consistent with very limited contribution of first cycle volcanogenic zircon to the Pampean eolian system, but abundances of older Neogene zircon indicate proto-sources in the Andes. The ríos Desaguadero, Colorado, and Negro contain populations that were likely within the dust production pathways of most of the loess, paleosol, and eolian dune deposits, but the derivation of the zircon ages in these sediments cannot be explained solely by these river systems. One statistical outlier, a loess sample from the Atlantic coast of the Pampa region, indicates quantitative similarity to the age spectra from the ríos Colorado and Negro, consistent with derivation from these subparallel rivers systems during subaerial exposure of the continental shelf under high global ice-volume. Another statistical outlier, a paleosol sample from the Río Paraná delta region, has zircon ages more closely associated with sediments in the Paraná region than in rivers south of the Pampa region. Collectively, these data point to the complexity of the Pampean eolian system and substantial spatial-temporal variation in this Pleistocene−Holocene eolian system.